The field of the disclosure relates generally to wind turbine generators and, more particularly, to control devices for use on wind turbine generators.
At least some known wind turbine generators include a rotor having multiple blades. The rotor is sometimes coupled to a housing, or nacelle, that is positioned on top of a base, for example, a truss or tubular tower. At least some known utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) have rotor blades having predetermined shapes and dimensions. The rotor blades transform mechanical wind energy into induced blade lift forces that further induce a mechanical rotational torque that drives one or more generators, subsequently generating electric power. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into the electric utility grid. Gearless direct drive wind turbine generators also exist.
During operation of such known wind turbines, a yawing device may be used to orient the wind turbine into the direction of the wind. Some known yawing devices include an electrical or hydraulic motor and a high-ratio gear that acts on the toothed path of the yaw bearing and thus turns the machinery into the desired position. Due to the influence of wind shear, for example, the machinery is subjected to pulsating forces, both when yawing and when the machinery is stationary. These forces often have a dominating tendency in one direction, which means that they tend to turn the wind turbine out of the direction of the wind.
Known yawing devices include a single input shaft that receives a torque from a motor located within the wind turbine, and translates this torque via a plurality of gearing assemblies to a single output torque shaft that facilitates yawing the wind turbine. However, because of the limited rotational force that can be applied by a single output shaft, numerous yawing devices are required within each wind turbine to supply the force needed to yaw the wind turbine, especially under less-than-optimal weather conditions, i.e. in high winds.